The invention relates to a method for winding a paper, board or material web on a winder of the two-drum type, and to a method for manufacturing a winding core for a winder, and a winding core for a winder.
In the prior art, slitter-winders are known in which winding takes place on winding drums after the slitting of a paper, board or material (e.g. plastic, aluminium, etc.) web. In winders of the two-drum type, slit component webs are wound around a winding core, e.g. a roll core, on support of two drums or one drum and a set of drums or two sets of drums. In the following description and claims, for the sake of simplicity, the term winding drum is used when referring to a carrier drum/a set of carrier drums in a winder of the two-drum type, i.e. including the meanings of both a winding drum and a set of winding drums. In addition, in the following description the term roll core is also partly used in the general sense ‘winding core’, i.e. by the term roll core is meant a winding core that is made of paper, board, glass fibre, metal, plastic, or the like.
In two-drum winders, in which narrower component webs slit with slitter blades from a web unwound from a machine reel are wound into customer rolls, the rolls are usually placed side by side on two winding drums. Because of variations in the cross-direction profiles, for example, thickness, moisture, roughness or friction, of the web to be wound, adjacent rolls are not always formed with precisely equally large diameters, in spite of the fact that precisely equally long component webs are wound into them. Owing to the different diameters of the rolls, the winding cores placed in the roll centers are displaced with the progress of winding in relation to one another so that their centers of rotation are separated and, at the same time, variations also occur in the angular speeds of the rolls. Because of this detrimental phenomenon there occurs vibration in two-drum winding, with the result that it is necessary to limit speed, i.e. to be content with a lower winding speed, which reduces the capacity of the machine and is, thus, uneconomical.
The problem described above has occurred as long as winders of the two-drum type have been constructed without a shaft, i.e. inside roll cores there is no shaft that couples them together. The seriousness of the problem has, however, varied in the course of the years, because the profile of the web produced on the paper machine has improved and a limited running speed has been accepted on the slitter-winder. In recent years, the diameters of the customer rolls produced have started becoming ever larger and, at the same time, the machine widths and the winding speeds have also increased, for which reason the problem of vibration has been noticed again: even a small variation of profile in the direction of width of the web is cumulated especially during winding of thin paper grades so that faults in the shape of the rolls which arise from the web profile cause a significant vibration problem.
In the winding process, a number of different phenomena are effective which attempt to shift the web rolls that are being formed in their axial direction:                deflection of winding cylinders, i.e. winding drums,        faults in the shape of the rolls arising from uneven profile of the web, and        also the core chucks, which support the winding cores of the outermost web rolls, subject the row of rolls to axial forces when they keep the row of rolls in the desired position.        
One problem in winding is also that the length of the winding cores, for example, roll cores, changes during winding because the compression pressure caused by the winding of the web onto the roll core causes widening of the wound web and elongation of roll cores.
The core chucks alone can also produce a compression force acting on the whole row of winding cores if the winding cores are excessively long: the total length of the winding cores is greater than the regulated distance between the core chucks.
When a paper or board web is wound around a roll core, in two-drum or carrier belt slitting the rolls and the roll cores are in a row and they are kept in place in the axial direction by means of core chucks. If there are cross direction thickness variations in the web, the rolls will have different diameters and, consequently, the roll cores are no longer on the same axis of rotation. This readily leads to the bouncing of rolls and the running speed must be lowered. In some places the situation has been helped by disposing sleeves between the roll cores to couple the roll cores together for the time of winding. However, the use of them causes additional work and makes the separation of the rolls more difficult after the winding.
One problem is that if the circumference of a roll changing in a winder is round in its outer surface but the roll core is not located at the centre line, this makes converting more difficult in which the roll is again supported at the center, because in such a case the roll starts to bounce. This also causes problems in that in converting, for example, in printing houses where roll change is accomplished as a flying splice change, the alignment of the web is generally monitored based on the edge and if the roll has not been formed properly in respect of the center, there will be a displacement of the web at the splice in connection with splicing.
In the course of the years, the rolls have become larger in size, diameter has increased and width has grown and, along with it, it has been necessary to make the roll cores still harder. Since during tight winding the roll cores nevertheless elongate, this elongation cumulates in the edge rolls and against the core chucks. To prevent the increase of the axial force of the roll chucks, the core chucks have been provided with flexibility but it increases the dishing of the edge rolls. Roll dishing occurs when a contracted web under tension is wound. The tension changes into a compression stress inside the roll, with the result that the web tends to become wider. This causes that the rolls push one another. The widening cumulates from the middle towards the edges.
The problems described above are most difficult when winding a web that has high compressibility and a high friction coefficient. Such web grades include, for example, DIP newsprint which is recycled fiber based newsprint, and sack paper. The degree of seriousness of the problem is affected, among other things, by where the recycled paper is derived from, what kind of deinking method has been used in its cleaning and what properties the recycled paper has.
With respect to the prior art, reference may be made to FI patent application 20002679, which discloses a method and a device for winding a paper or board web and proposes an arrangement for the problems described above and, in particular, for determining the compression pressure and the position of core chucks in the winding process, in which arrangement measuring devices for measuring the position and the force of the chuck as well as machine controls for controlling the core chuck are arranged in connection with the core chuck such that the position and/or the force of the chucks is in a desired value range, i.e. within desired limits, and no harmful vibration is generated because of axial thrust forces of detrimental magnitude between the winding cores. It is stated that in this method according to the invention it is novel and inventive that in the method the winding cores are placed in a desired position and subjected to a desired compression force by means of the core chucks, the length of the row of the winding cores is determined and the compression force of at least one core chuck is regulated during winding when the length of the row of the winding cores changes to keep the compression force and/or the length of the winding core row within desired limits.
With respect to the prior art, reference may also be made to FI patent No. 103103, which discloses a method in winding, wherein a number of separate rolls are formed around separate winding cores placed one after the other while supported by support members, in an attempt to solve the problems described above, in particular in connection with different vibration problems. It is stated that a new idea in this method is that, in order to reduce the friction coefficient of the winding cores, before, or at the same time as, the winding cores are placed in the winding position, the ends of the winding cores are treated with an agent that reduces the friction coefficient, or a piece of a material that has a low friction coefficient is placed at the ends of the winding cores, and/or the axial thrust force between the winding cores is lowered by passing a pressurized medium through the core chucks and allowing it to discharge from between the winding cores.